The present invention relates to a display device having a pair of substrates opposed to each other and a pixel region formed between the substrates, such as a liquid crystal display (LCD) driven by various transistors such as thin film transistors (TFTs), and also relates to a manufacturing method for the display device.
In recent years, a display device has been required to provide high-definition and high-quality display. As a liquid crystal display meeting this requirement, an active matrix type liquid crystal display using TFTs is used. The TFTs are used as switching elements for driving a liquid crystal.
FIG. 4 shows a plan view of a liquid crystal display in the related art. The liquid crystal display includes a pixel region S having a plurality of pixels arranged in a matrix form for displaying an image, and a peripheral circuit region R arranged so as to surround the pixel region S.
Usually, an active matrix type liquid crystal display using TFTs has a control unit for sending a control signal to each TFT and a lead wiring connected to the control unit. In many cases, the lead wiring is located in a region of the liquid crystal display other than the pixel region S, that is, in the peripheral circuit region R. This arrangement is used in many LCDs at present.
The manufacture of an active matrix type liquid crystal display using TFTs is generally classified into a manufacturing process for a drive substrate on which the TFTs are formed and a manufacturing process for another substrate opposed to the drive substrate. These substrates are aligned and attached to each other to define a gap therebetween, and a liquid crystal is filled into this gap.
The drive substrate manufacturing process includes the steps of first forming a silicon oxide film or a silicon nitride film as a gate insulating film of each TFT on a translucent substrate such as a glass substrate, next forming a silicon oxide film or a silicon nitride film as an interlayer insulating film, next forming a metal film of Al (aluminum) as a lead wiring, and finally patterning the metal film to form the lead wiring. Another interlayer insulating film is usually formed over the lead wiring.
The lead wiring is formed on the interlayer insulating film covering the TFTs as described in Japanese Patent Laid-open Nos. 2001-242803 and 2001-284592 and Japanese Patent No. 3247793, for example. An example of the arrangement of a conventional lead wiring 14 is shown in FIG. 5. As shown in FIG. 5, the conventional lead wiring 14 is formed on an interlayer insulating film 13. Accordingly, the height of the lead wiring 14 from the substrate is about 0.5 μm to 1 μm in many cases.
Thus, the conventional lead wiring is disposed at a height of about 0.5 μm to 1 μm from the substrate, so that the lead wiring is prone to damage by an external pressure. Particularly in the manufacturing process for an active matrix type liquid crystal display using TFTs, it is necessary to align a pair of substrates (glass substrates) and to remove a part of one of the substrates, so as to provide an extension of the other substrate on which the lead wiring is to be formed. At this time, an undue pressure may be frequently applied to the lead wiring formed on the extension.
Further, in the manufacturing process for an active matrix type liquid crystal display using TFTs, there is a possibility that a worker may touch the lead wiring, causing damage (scratches) to the lead wiring. The damage to the lead wiring may cause a break in the lead wiring during conduction of electricity due to electromigration, temperature, etc., thus leading to a reduction in reliability of the display device.